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照射後試験用渦電流探傷技術の開発,2; 高燃焼度照射燃料ピン試験結果

Development of eddy current testing technique for irradiated fuel pins, 2; ECT results of irradiated fuel pins of high burn up

宮地 紀子; 永峯 剛; 勝山 幸三

Miyaji, Noriko; Nagamine, Tsuyoshi; Katsuyama, Kozo

照射された高速炉用燃料ピン被覆管の健全性を非破壊にて確認するために、渦電流探傷技術の開発を行っている。本試験では、15Ni-15Cr-Ti鋼非照射模擬燃料被覆管及び「常陽」で照射した同仕様の燃料ピンを対象に、被覆管内面腐食探傷を目的として、渦電流探傷試験を実施した。非照射模擬燃料被覆管の腐食探傷の結果、周波数32kHzを用いて腐食箇所を探傷できる結果を得た。また、被覆管肉厚と渦電流信号には相関があり、肉厚が小さくなると信号は大きくなる傾向を示した。「常陽」で照射した燃料ピンの渦電流探傷試験の結果、腐食が小さく、渦電流信号からは腐食箇所を確認することはできなかった。しかし本試験では、冷却材であるナトリウムによる被覆管外面の腐食が信号に影響を及ぼしていることが示唆された。また、照射による被覆管の電磁気的特性の変化に加えて、FPガスやPCMI(ペレットと被覆管の機械的相互作用)による被覆管内圧も信号に影響を及ぼす可能性が高いことが示唆された。

Eddy current testing (ECT) technique has been developed in order to check the soundness of irradiated fuel pins non-destructively. This paper describes the results that it was examined if corrosions were detected using an imitation fuel pin, made of 15Ni-15Cr-Ti and same type of the fuel pins irradiated in JOYO. As the results of experimental for an imitation pin, ECT detected the corrosions using frecquency 32kHz. And, the signal of eddy current became larger as the thickness of the cladding became smaller, because there was some correlation between the signal and thickness. As for the irradiated fuel pins, inner corrosions were not recognized from the signal because their sizes were too small. However, outside corrosions by sodium as coolant might have an influence on the signal. And, as well as a change of the electromagnetic characteristics of cladding by irradiation, inner pressure by FP gas and PCMI might have an influence on the signal.

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